Fontconfig is a library designed to provide a list of available fonts to applications, and also for configuration for how fonts get rendered. See package fontconfig and Wikipedia:Fontconfig. The Free type library (freetype2 package) renders the fonts, based on this configuration.

Though Fontconfig is the standard in today's Linux, some applications still rely on the original method of font selection and display, the X Logical Font Description.

The font rendering packages on Arch Linux includes support for freetype2 with the bytecode interpreter (BCI) enabled. Patched packages exist for better font rendering, especially with an LCD monitor. See #Patched packages below. The #Infinality package allows both auto-hinting and subpixel rendering, allows the LCD filter to be tweaked without recompiling, and allows the auto-hinter to work well with bold fonts.

Font paths

For fonts to be known to applications, they must be cataloged for easy and quick access.

The font paths initially known to Fontconfig are: /usr/share/fonts/ and ~/.fonts/ (of which Fontconfig will scan recursively). For ease of organization and installation, it is recommended to use these font paths when adding fonts.

To see a list of known Fontconfig fonts:

$ fc-list : file

See man fc-list for more out put format.

Check for Xorg's known font paths by reviewing its log:

$ grep /fonts /var/log/Xorg.0.log

Tip: You can also check the list of Xorg's known font paths using the command xset q.

Keep in mind that Xorg does not search recursively through the /usr/share/fonts/ directory like Fontconfig does. To add a path, the full path must be used:

Section "Files"
FontPath "/usr/share/fonts/local/"
EndSection

If you want font paths to be set on a per-user basis, you can add and remove font paths from the default by adding the following line(s) to ~/.xinitrc:

Fontconfig configuration

Configuration can be done per-user through $XDG_CONFIG_HOME/fontconfig/fonts.conf, and globally with /etc/fonts/local.conf. The settings in the per-user configuration have precedence over the global configuration. Both these files use the same syntax.

Note: Configuration files and directories: ~/.fonts.conf, ~/.fonts.conf.d and ~/.fontconfig/*.cache-* are deprecated since fontconfig 2.10.1 (upstream commit) and will not be read by default in the future versions of package. Use instead $XDG_CONFIG_HOME/fontconfig/fonts.conf, $XDG_CONFIG_HOME/fontconfig/conf.d and $XDG_CACHE_HOME/fontconfig/*.cache-* respectively. If you use the second directory, the file must follow the naming convention NN-name.conf (where NN it's a two digit number like 00, 10, or 99).

Fontconfig gathers all its configurations in a central file (/etc/fonts/fonts.conf). This file is replaced during fontconfig updates and shouldn't be edited. Fontconfig-aware applications source this file to know available fonts and how they get rendered. This file is a conglomeration of rules from the global configuration (/etc/fonts/local.conf), the configured presets in /etc/fonts/conf.d/, and the user configuration file ($XDG_CONFIG_HOME/fontconfig/fonts.conf).

Note: For some desktop environments (such as GNOME and KDE) using the Font Control Panel will automatically create or overwrite the user font configuration file. For these desktop environments, it is best to match your already defined font configurations to get the expected behavior.

Presets

There are presets installed in the directory /etc/fonts/conf.avail. They can be enabled by creating symbolic links to them, both per-user and globally, as described in /etc/fonts/conf.d/README. These presets will override matching settings in their respective configuration files.

Anti-aliasing

Font rasterization converts vector font data to bitmap data so that it can be displayed. The result can appear jagged due to aliasing. anti-aliasing is enabled by default and increases the apparent resolution of font edges.

Hinting

Font hinting (also known as instructing) is the use of mathematical instructions to adjust the display of an outline font so that it lines up with a rasterized grid, such as the pixel grid in a display. Fonts will not line up correctly without hinting until displays have 300 DPI or greater. Two types of hinting are available.

Byte-Code Interpreter (BCI)

Using normal hinting, TrueType hinting instructions in the font are interpreted by freetype's Byte-Code Interpreter. This works best for fonts with good hinting instructions.

Autohinter

Auto-discovery for hinting. This looks worse than normal hinting for fonts with good instructions, but better for those with poor or no instructions. The autohinter and subpixel rendering are not designed to work together and should not be used in combination.

Hint style

Hint style is the amount of influence the hinting mode has. Hinting can be set to: hintfull, hintmedium, hintslight and hintnone. With BCI hinting, hintfull should work best for most fonts. With the autohinter, hintslight is recommended.

Subpixel rendering

Subpixel rendering effectively triples the horizontal (or vertical) resolution for fonts by making use of subpixels. The autohinter and subpixel rendering are not designed to work together and should not be used in combination without the #Infinality patch set.

Most monitors manufactured today use the Red, Green, Blue (RGB) specification. Fontconfig will need to know your monitor type to be able to display your fonts correctly.

If you notice unusual colors around font's borders, the wrong subpixel arrangement might be configured. The Lagom subpixel layout test web page can help identify it.

LCD filter

When using subpixel rendering, you should enable the LCD filter, which is designed to reduce colour fringing. This is described under LCD filtering in the FreeType 2 API reference. Different options are described under FT_LcdFilter, and are illustrated by this LCD filter test page.

The lcddefault filter will work for most users. Other filters are available that can be used in special situations: lcdlight; a lighter filter ideal for fonts that look too bold or fuzzy, lcdlegacy, the original Cairo filter; and lcdnone to disable it entirely.

Advanced LCD filter specification

If the available, built-in LCD filters are not satisfactory, it is possible to tweak the font rendering very specifically by building a custom freetype2 package and modifying the hardcoded filters. The Arch Build System can be used to build and install packages from source.

First, refresh the freetype2 PKGBUILD as root:

# abs extra/freetype2

This example uses /var/abs/build as the build directory, substitute it according to your personal ABS setup. Download and extract the freetype2 package as a regular user:

Reboot or restart X. The lcddefault filter should now render fonts differently.

Disable auto-hinter for bold fonts

The auto-hinter uses sophisticated methods for font rendering, but often makes bold fonts too wide. Fortunately, a solution can be turning off the autohinter for bold fonts while leaving it on for the rest:

Replace fonts

The most reliable way to do this is to add an XML fragment similar to the one below. Using the "binding" attribute will give you better results, for example, in Firefox where you may not want to change properties of font being replaced. This will cause Ubuntu to be used in place of Georgia:

Disable scaling of bitmap fonts

To disable scaling of bitmap fonts (which often makes them blurry), remove /etc/fonts/conf.d/10-scale-bitmap-fonts.conf.

Create bold and italic styles for incomplete fonts

Freetype has the ability to automatically create italic and bold styles for fonts that do not have them, but only if explicitly required by the application. Given programs rarely send these requests, this section covers manually forcing generation of missing styles.

Start by editing /usr/share/fonts/fonts.cache-1 as explained below. Store a copy of the modifications on another file, because a font update with fc-cache will overwrite /usr/share/fonts/fonts.cache-1.

Tip: Use the value 'embolden' for existing bold fonts in order to make them even bolder.

Change rule overriding

Fontconfig processes files in /etc/fonts/conf.d in numerical order. This enables rules or files to override one another, but often confuses users about what file gets parsed last.

To guarantee that personal settings take precedence over any other rules, change their ordering:

# cd /etc/fonts/conf.d
# mv 50-user.conf 99-user.conf

This change seems however to be unnecessary for the most of the cases, because a user is given enough control by default to set up own font preferences, hinting and antialiasing properties, alias new fonts to generic font families, etc.

Pseudo Gamma Correction: Lighten and darken glyphs at a given value, below a given size. Works on native TT hinter and autohinter.

Embolden Thin Fonts: Embolden thin or light fonts so that they are more visible. Works on autohinter.

Force Slight Hinting: Force slight hinting even when programs want full hinting. If you use the local.conf I provide (included in infinality-settings fedora package) you will notice nice improvements on @font-face fonts.

ChromeOS Style Sharpening: ChromeOS uses a patch to sharpen the look of fonts. This is now included in the infinality patchset.

A number of presets are included and can be used by setting the USE_STYLE variable in /etc/profile.d/infinality-settings.sh.

Note: The user bohoomil maintains a very good configuration in his github repo which is available as a package in the AUR.

It is recommended to also install fontconfig-infinalityAUR to enable selection of predefined font substitution styles and antialiasing settings, apart from the rendering settings of the engine itself. After doing so, you can select the font style (win7, winxp, osx, linux, ...) with:

# infctl setstyle

If you set e.g. win7 or osx you need the corresponding fonts installed.

Note: Default infinality settings can cause some programs to display fonts at 72 DPI instead of 96. If you notice a problem open /etc/fonts/infinality/infinality.conf search for the section on DPI and change 72 to 96. This problem can specifically affect conky causing the fonts to appear smaller than they should. Thus not aligning properly with images.

Note: The README for fontconfig-infinalityAUR says that /etc/fonts/local.conf should either not exist, or have no infinality-related configurations in it. The local.conf is now obsolete and completely replaced by this configuration.

Infinality: the easy way

bohoomil also maintains infinality-bundle repository, offering three basic libraries (freetype2-infinality-ultimate, fontconfig-infinality-ultimate & cairo-infinality-ultimate) as pre-patched, pre-configured and pre-built binaries for all architectures (i686, x86_64, multilib). Using infinality-bundle makes the whole installation & configuration process dramatically simplified: all one has to do is install the three packages with

# pacman -S infinality-bundle

which will replace the corresponding, generic Arch libraries (i.e. freetype2-infinality-ultimate will be used instead of freetype2, fontconfig-infinality-ultimate instead of fontconfig and fontconfig-infinality-ultimate from the AUR, and cairo-infinality-ultimate instead of the regular cairo). The libraries are fully compatible with the Arch packages and are meant to be used as drop-in replacements for them. No post installation/upgrade steps are required for most use scenarios: everything should work out of the box.

Reverting to unpatched packages

To restore the unpatched packages, reinstall the originals:

# pacman -S --asdeps freetype2 cairo fontconfig

Applications without fontconfig support

Some applications like URxvt will ignore fontconfig settings. This is very apparent when using the infinality patches which are heavily reliant on proper configuration. You can work around this by using ~/.Xresources, but it is not nearly as flexible as fontconfig. Example (see #Fontconfig configuration for explanations of the options):

Make sure the settings are loaded properly when X starts with xrdb -q (see Xresources for more information).

Troubleshooting

Distorted fonts

Note: 96 DPI is not a standard. You should use your monitor's actual DPI to get proper font rendering, especially when using subpixel rendering.

If fonts are still unexpectedly large or small, poorly proportioned or simply rendering poorly, fontconfig may be using the incorrect DPI.

Fontconfig should be able to detect DPI parameters as discovered by the Xorg server. You can check the automatically discovered DPI with xdpyinfo (provided by the xorg-xdpyinfo package):

$ xdpyinfo | grep dots

resolution: 102x102 dots per inch

If the DPI is detected incorrectly (usually due to an incorrect monitor EDID), you can specify it manually in the Xorg configuration, see Xorg#Display Size and DPI. This is the recommended solution, but it may not work with buggy drivers.

Fontconfig will default to the Xft.dpi variable if it is set. Xft.dpi is usually set by desktop environments (usually to Xorg's DPI setting) or manually in ~/.Xdefaults or ~/.Xresources. Use xrdb to query for the value:

$ xrdb -query | grep dpi

Xft.dpi: 102

Those still having problems can fall back to manually setting the DPI used by fontconfig:

Calibri, Cambria, Monaco, etc. not rendering properly

Some scalable fonts have embedded bitmap versions which are rendered instead, mainly at smaller sizes. Force using scalable fonts at all sizes by #Disabling embedded bitmap.

Older GTK and QT applications

Modern GTK apps enable Xft by default but this was not the case before version 2.2. If it is not possible to update these applications, force Xft for old GNOME applications by adding to ~/.bashrc:

export GDK_USE_XFT=1

For older QT applications:

export QT_XFT=true

Applications overriding hinting

Some applications may override default fontconfig hinting and anti-aliasing settings. This may happen with Gnome 3, for example. Use the specific configuration program for the application in such cases. For gnome, try gnome-tweak-tool.